Low-power CDMA receiver

ABSTRACT

A first amplifier amplifies a radio frequency signal into a first stage signal, a detector produces a bypass signal based on the environment in which the receiver is operating. A switch provides the first stage signal or the first stage signal filtered by a radio frequency filter based on the bypass signal is not asserted. Optionally, the detector also produces a bias control signal and bias generators set the bias levels of the amplifiers according to the bias control signal. The invention increases linear range RF amplification stages. Power consumption is reduced by reducing the amplification (and optionally the bias levels) used under typical conditions. The invention is advantageous for applications where power is at a premium and the receiver, or at least its front end, operates while the device is in standby mode. Such applications include mobile, portable and hand held pagers and wireless telephones and Internet connections.

RELATED APPLICATIONS

This application relates to U.S. patent application Ser. No. 09/538,606,filed Mar. 29, 2000, entitled “Low Power and High Linearity Receiverswith Reactively Biased Front Ends” by the same inventor and assigned tothe same assignee.

FIELD OF THE INVENTION

The invention relates to the design of electronic amplifiers forreceivers. In particular, it relates to achieving low power and highlinearity receiver amplifiers by means of reactively switching in andout both the amplification and filtering stages.

BACKGROUND OF THE INVENTION

An electronic amplifier accepts as its input an electronic signal andproduces as its output a stronger version of that electronic signal. Forexample, recording an electrocardiogram on a chart requires amplifyingthe weak electrical signal produced by a beating heart until the signalis strong enough to move a pen up and down as a paper chart moves pastthe pen.

A linear amplifier is one in which there is a linear relationshipbetween the electronic signal it receives as input and the electronicsignal it produces as output. That is, for a change of X units in itsinput voltage or current, it produces a change in its output voltage orcurrent of k*X (k times X) units for some constant value k, regardlessof whether the value of the input signal is small or large.

Every electronic circuit is unable to product outputs larger than somelimit. Every electronic circuit is unable to effectively handle inputslarger than some limit or smaller than some other limit. Nevertheless,for many applications of electronic circuits, it is necessary that theybe operated only within a middle range where they produce a linearresponse to changes in their inputs.

Common examples of practical applications where linear amplifiers areused include both audio amplifiers and radio-frequency amplifiers. Ifyou listen to an audio amplifier that is not linear in its response,then you hear the music or voice as distorted or flat.

Non-linear responses in radio-frequency amplifiers can produce crosstalk or intermodulation between the desired signal and anotherextraneous radio signal that happens to be present at the same time, buton a different frequency or channel. Such undesired signals are calledjamming sources whether or not the interference is intentional. When anamplifier behaves non-linearly, for example, a change of X in its inputsignal produces less than k*X change in its output signal, then theeffect of this non-linearity is to shift the frequency of the signalthat it amplifies. If a desired signal and a jamming source at differentfrequencies are present at the same time (which is typical of theoperating environment for radio receivers), then this frequency shiftresults in cross talk or intermodulation between the two signals.

Many electronic amplifiers electrically combine their input signal witha constant or bias voltage or current. The amount of bias used is chosenin order to set an appropriate operating point for the amplifier. Whenan electronic amplifier is designed, an important choice is whether tomake that constant bias have a relatively large or a relatively smallvalue. The bias value chosen when designing the amplifier can have majorconsequences on how and how well it operates.

One standard technique in designing a linear amplifier is to firstspecify the range of the input signal over which the amplifier mustrespond linearly and the degree to which the amplifier must rejectintermodulation from undesired sources. Then, the amount of bias currentor voltage is set so as to meet to these specifications. The larger therange of linearity desired and the lower the amount of intermodulationthat is acceptable, then the larger the bias must be.

Unfortunately, the larger the bias of an amplifier, the more power itconsumes. Thus, there is a tradeoff between an amplifier's powerconsumption on the one hand and its range of linearity andsusceptibility to intermodulation on the other hand. The design goal ofminimizing power consumption opposes the design goal of maintainingacceptable linearity.

Power conservation is always desirable. But with the advent of widelyused mobile, hand-held and pocket wireless devices, such as pagers andcellular telephones, its importance has increased.

The radio-frequency amplifiers, buffers and other front-end circuitry ina pager or in the receiver section of a cellular or other mobiletelephone must be operating in order for the device to respond to a pageor phone call broadcast to it. Thus, the length of time that a batterywill last while the device is standing by for a page or a phone calldepends on how much power is consumed by its receiver. To manyconsumers, most of the power consumed by the device is consumed instandby mode—for example, a mobile phone may be standing by for a callmany hours each day but in use for calls only minutes each day.

Longer battery life reduces the costs and increases the convenience forconsumers who use, for example, portable devices, including but notlimited to mobile devices, hand held devices, pagers, mobile phones,digital phones, PCS phones and AMPS phones. In these highly competitivemarkets, battery life in standby mode can make the difference as towhich competing product the consumer chooses. Thus, it is critical forthe market success of mobile, portable and hand-held receivers that theyconsume a minimum of power, particularly in standby mode.

The standby battery life of a mobile receiver can be significantlyincreased by lowering its power consumption by lowering the bias levelused in its front-end circuits such as amplifiers and buffers. However,prior art techniques for doing this also reduce the receiver's linearrange and thus increase its susceptibility to intermodulation fromjamming sources.

SUMMARY OF THE INVENTION

Thus, there is a need for a linear amplifier for receivers in whichpower consumption can be decreased without reducing linearity orincreasing intermodulation susceptibility. This need can be met byswitching both filtering stages and amplification stages in or outdepending on signal strength. This need can also be met by reactivelyadjusting the bias level at which the amplifier operates, i.e. byincreasing its bias level in reaction to strong signal environments.

One embodiment of the invention includes methods and apparatuses for areceiver with an amplifier that amplifies a radio frequency signal intoa first stage signal, a detector that produces a bypass signal only whena first signal strength is sufficiently strong, a switch that providesthe first stage signal when the bypass signal is asserted, and thatprovides the first stage signal filtered by a radio frequency filter andamplified by a second amplifier when the bypass signal is not asserted.

Another embodiment of the invention includes methods and apparatuses fora radio frequency receiver with a first amplifier that amplifies aninput signal into a first stage signal, a detector that produces abypass signal only when the first signal strength of the receiver issufficiently strong, a switch that provides the first stage signal whenthe bypass signal is asserted and provides the first stage signalfiltered by a radio frequency filter and amplified by a second amplifierwhen the bypass signal is not asserted, and bias generators for thefirst and the second amplifiers that generate bias levels based on asecond signal strength of the receiver, or optionally on the bypasssignal.

Optionally, the bias levels are adjusted to condition them, to scalethem, to respond to the bias levels as regulating feedback, to hold themat a particular level when the receiver is operating under an idlecondition, and to hold them at a particular level when the receiver isoperating under an idle condition and generally increase them as thesignal strength increases.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are illustrated in the followingdrawings, in which known circuits are shown in block-diagram form forclarity. These drawings are for explanation and for aiding the reader'sunderstanding. The invention should not be taken as being limited to theembodiments and design alternatives illustrated.

FIG. 1 shows the building blocks, or functional components, that make upone embodiment of the invention. This embodiment is a receiver amplifierthat adjusts its own bias level in reaction to the current signalstrength within its environment. It also shows the interconnections ofthese functional components.

FIG. 2A shows electronic circuit components and their interconnectionsthat can be used to make each of the functional components shown in theprevious figure. The embodiment of the invention shown is suitable forsmall signal or low noise applications. Also, this embodiment issuitable for a modular, multi-stage embodiment of the invention. Thefunctional component shown as variable resistance 204-A in FIG. 2A canbe replaced with variable resistance 204-B in FIG. 2B or with variableresistance 204-C in FIG. 2C.

FIG. 3 shows the electronic circuit components and theirinterconnections for another embodiment of the invention, specifically asimplified self-adjusting RF amplifier.

FIG. 4 shows the electronic circuit components and theirinterconnections for an embodiment of the invention, specifically aself-adjusting IF amplifier.

FIG. 5 shows the functional components and their interconnections foryet another embodiment of the invention. This embodiment is the firststages of a receiver within a mobile device such as a cellular or othermobile telephone. This embodiment has multiple stages of amplificationand one stage of frequency conversion, where each stage self-adjusts itsown bias level. FIG. 5 also shows the functional components and theirinterconnections for an embodiment of the invention in a transceiver,i.e. a device that both transmits and receives.

FIG. 6 shows the functional components and their interconnections foranother embodiment of the invention. This embodiment is the first stagesof a receiver with multiple stages of active circuits such asamplifiers, where the bias level used within each stage is adjusted by asingle signal level detector and a single bias adjustment circuit.

FIG. 7 shows the functional components and their interconnections foranother embodiment of the invention. This embodiment is the first stagesof a receiver in which a first filter and an RF amplifier are optionallyincluded in the receiver's signal path or switched out of it.

FIGS. 8 shows electronic circuit components and their interconnectionsthat can be used to make another embodiment of the invention that uses asample and hold circuit that can improve the accuracy of the reactivebias function by compensating for variations in the threshold of circuitcomponents.

FIG. 9 shows how one embodiment of the invention can be made with manyof its electronic circuit components formed using a single integratedcircuit with 10 pins.

FIG. 10 shows the functional components and their interconnections foranother embodiment of the invention. This embodiment is the first stagesof a receiver that uses the integrated circuit of the previous figure tobuild a receiver that can be operated in several modes used in mobiletelephone applications. These modes include analog modes such ascellular and advanced mobile phone service (AMPS) as well as digitalmodes such as code division multiple access (CDMA) and personalcommunication service (PCS).

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein are various alternative embodiments of and alternativedesigns for the invention. The invention, however, should not be takenas being limited to the embodiments and alternatives described. Oneskilled in the art will recognize still other alternative embodimentsand designs, as well as various changes in form and detail. These may beemployed while practicing the invention without departing from itsprinciples, spirit or scope.

FIG. 1 is a functional block diagram of receiver amplifier 100 accordingto one embodiment of the invention. This amplifier has reactive biasing,i.e. it adjusts its bias level in reaction to the signal strength withwhich it is currently operating.

RF/IF receiver amplifier 101 amplifies input signal 120 into outputsignal 121. The bias of amplifier 101 is set by bias level 143, which isproduced by bias generator 103.

RF/IF receiver amplifier 101 can be any type of linear amplifier withcharacteristics suitable for radio-frequency (RF), intermediatefrequency (IF), or other applications. RF/IF receiver amplifier 101 canbe, but is not limited to, a common emitter amplifier, a common baseamplifier, a common collector amplifier, a voltage amplifier, a currentamplifier, a transconductance amplifier, a transresistance amplifier, anamplifier with feedback, or an amplifier without feedback. In someembodiments of the invention, reactive biasing is applied only to RFstages, or only to some of the initial RF stages, and the bias levels onIF stages are fixed according to conventional techniques.

As shown in FIG. 1, level detector 102 detects the signal level of RF/IFoutput signal 121, and thus it indirectly detects the signal level ofRF/IF input signal 120. Alternatively, level detector 102 can directlydetect the signal level of RF/IF input signal 120 or of an intermediatesignal between the input and the output signal. Level detector 102produces bias control signal 140 according to the signal level that itdetects.

Level detector 102 can be any type of circuit that is able to detectchanges, over an appropriate time frame, in the signal level with whichthe receiver is currently operating. For example, level detector 102 canbe a rectifier, or a heat generator of some type coupled to a heatmonitor such as a thermistor.

The detected signal level can indicate an averaged signal level thatdepends on the signal environment in which the receiver is currentoperating, with the average being taken over a suitable period of time.Generally, the frequency of bias level 143 should be limited to beorders of magnitude lower than the frequency of the signal of interest.As a first example, a 2 MHz response in bias level may provide anappropriate time frame over which to average the signal level and adjustthe bias level for a 2 GHz carrier signal such as is used in acode-division multiple access (CDMA) signal.

Also, consideration should be given to the possibility of spurioussidebands arising between the bandwidth of the bias level transferfunction and the bandwidth of the signal of interest. To continue withthe CDMA example where the desired CDMA signal has a bandwidth limitedto 1.25 MHz, a response in bias level limited to being near 2 MHz maykeep any such sidebands out of the receiver's bandwidth, and thusminimize interference with the CDMA signal.

Alternatively, the response in bias level could be limited to beingbelow the receiver's bandwidth. As a second example, a 100 Hz biasadjustment response may minimize interference with a voice signallimited to between 500 and 3,000 Hz. However, limiting the frequency ofbias level 143 to be below the range of the signal of interest mayundesirably slow down the response time of the receiver to changes insignal strength. This could be significant to system performance if thecurrent signal environment includes a jamming signal that is onlyintermittently present.

Thus, bias level 143 should be able to vary quickly enough that theperformance of the overall system in which the reactively biasedamplifier is used is not harmed by a lag or hysteresis effect, such asmight occur when a high-signal environment changes to a low-signalenvironment, or visa versa.

Bias generator 103 produces bias level 143 according to the appropriatebias control signal. If bias adjustment circuit 105 is used, then biasgenerator 103 varies bias level 143 according to adjusted bias controlsignal 141, otherwise bias control signal 140 is used. Bias generator103 can be any circuit that varies bias level 143 within a target rangeaccording to the appropriate bias control signal.

In amplifiers with reactive biasing, level detector 102 and biasgenerator 103 to operate such that the bias applied to RF/IF receiveramplifier 101tends to increase as the input/output signal levelsincrease, i.e. as the receiver is used in an environment having strongersignal conditions. However, this increase need not be a linear or evenmonotonic increase. In some designs, the bias level may only generallytend to increase as the signal level increases. Preferably, this generaltendency to increase is sufficient to keep RF/IF receiver amplifieroperating with sufficient linearity and intermodulation rejection forthe particular application.

In embodiments of the invention that use bias adjustment circuit 105, itadjusts, filters, amplifies and/or conditions bias control signal 140into adjusted bias control signal 141, which is then used by biasgenerator 103 to generate bias level 143. The adjustment or adjustmentsapplied may include any transfer function, preferably but notnecessarily monotonic, including but not limited to conditioning,filtering, clipping, expanding, amplifying, dampening, scaling,offsetting, band limiting, sampling and holding and/or summing with anDC offset.

Bias adjustment circuit 105 can also include circuitry that compensatesfor threshold variations of active devices within the reactive biasingsystem, including but not limited to variations in the threshold of itsfield effect transistors (FETs). Because the linear range of a FET maybe narrow, it may be important to calibrate or set the levels used so asto maintain the circuit's operation within that linear range.

Bias adjustment circuit 105 could be any circuit that produces adjustedbias control signal 141 as a function of bias control signal 140. Ifregulating feedback signal 142 is used, then bias adjustment circuit 105can also vary bias level 143 according to regulating feedback signal142.

Various embodiments of bias adjustment circuit 105 include but are notlimited to circuitry that conditions bias control signal 140, that scaleit, that compare it against a reference level, that samples and holdsappropriate levels so as to calibrate a reference level corresponding toa given signal environment (such as an environment that is relativelyfree of jamming signals). Other embodiments include combinations of suchcircuitry.

In embodiments of the invention that use variable resistance 104, it canfunction as a circuit element within bias generator 103. By varying itsresistance, variable resistance 104 alters bias level 143. Variableresistance 104 could be any circuit that varies its resistance as afunction of control signal 140, or of adjusted bias control signal 141when available. Variable resistance 104 can be employed within biasgenerator 103 so as to vary the current of bias level 143, so as to varythe voltage of bias level 143, or both.

In embodiments of the invention that use bias feedback signal 142, itcan simply be bias level 143, or it can be a signal derived from biaslevel 143 or a signal that is a predecessor of bias level 143. Its useis optional, but it increases the stability of bias level 143,particularly when the circuit is operated under a wide range of voltageor temperature conditions, or when manufacturing tolerances of biasgenerator 103 or of other portions of the receiver have a significantimpact on bias level 143 or on what bias level 143 should be set to.Embodiments of the invention that use bias feedback signal 142 can alsobe somewhat self calibrating as to the amount of variation produced inbias level 143.

In some embodiments of the invention, the distinctions between leveldetector 102, bias adjustment circuit 105 and bias generator 103 breakdown and particular circuit components operate to produce multiplefunctions.

It is possible, and may be desirable in some applications, for onedetector to provide a bias control signal to multiple conditioners, orfor one bias adjustment circuit to provide a bias control signal tomultiple bias generators.

Reactive biasing allows amplifier 100 to be designed such that its powerconsumption in typical signal environments is decreased without reducingits linearity or intermodulation immunity in strong signal environments.Amplifier 100 can be designed with a bias level that is low, relative tothe maximum signal environment it might be used in. Then, when it isused in a strong signal environment, it adjusts its bias upwards, whichincreases its linearity and intermodulation immunity during the periodof time that the strong signal environment is present.

Such a linear amplifier with low power consumption in typical signalenvironments is particularly advantageous for mobile, hand held orpocket devices such as pagers, telephones or wireless data connections.With the advent of such devices, it has become critical to design linearamplifiers that consume as little power as possible while waiting for asignal that is addressed to them. This waiting mode may dominate theusage cycle of such devices, thus power savings during this mode mayhave a significant impact on battery life.

The RF and IF amplifiers in a cellular telephone, pager or data receivermust be operating in order for the device to respond to a phone call,page, e-mail or other transmission that is broadcast to them. Thus, thelength of time that a battery will last while the device is standing byfor a transmission addressed to the device depends on how much power isconsumed by the amplifiers and other circuits in its receiver section.

The power consumption of some mobile devices can be significantlyreduced by using amplifiers, buffers, mixers and other circuits thatembody the invention in the mobile device's receiver. In someapplications, the invention significantly increases the length of timethat a battery lasts when the mobile device is in standby mode.

Many mobile devices are in standby mode much of the time. For example, amobile telephone user may have their phone on ten hours a day, of whichonly {fraction (1/2 )} hour is spent actually using a phone connection.In this case, their cellular, PCS, amps or other mobile phone spends9{fraction (1/2 )} hours a day only receiving, i.e. listening for a calldirected to them, and {fraction (1/2 )} hour per day both receiving andtransmitting. In such a usage pattern, the phone's receiver section isactive 19 times longer than its transmitter section. Thus, receiverpower reduction can substantially reduce having to change or rechargebatteries or other energy storage devices in the mobile device, whichcan produce a corresponding gain in user convenience and reduction inuser expense.

In some embodiments of the invention, reactive biasing can allow linearamplifier 101 to be designed such that its linearity and intermodulationimmunity are increased. When such an amplifier is used in a strongsignal environment, it adjusts its own bias upwards, thus increasing itslinearity and intermodulation immunity. Rather than utilizing reactivebiasing for reducing the receiver's power consumption, these embodimentsof the invention utilize it for increasing the receiver's range oflinearity.

FIG. 2A is a circuit diagram of a small-signal or low-noise radiofrequency (RF) reactively biased receiver amplifier according to oneembodiment of the invention.

FIG. 2A shows the amplifier's components partitioned into functionalblocks corresponding to those shown in the previous figure. Thoseskilled in the art will recognize that there are numerous ways ofimplementing each of these functional blocks and that other ways will bedeveloped. These are all within the principles, spirit and scope of theinvention.

The variable resistance block within amplifier 200 can be implemented invarious ways, including but not limited to variable resistance 204-A,shown in FIG. 2A, variable resistance 204-B, shown in FIG. 2B, andvariable resistance 204-C, shown in FIG. 2C.

The components of the amplifier of FIG. 2A, their preferred values andtheir functional descriptions are given by the following table:

TABLE 1 Components of Low Noise, Reactively Biased RF AmplifierReference Suitable Designator Value Function RF Amplifier 201 C1 ˜1.0-22pF RF tuning and DC block capacitor C2 ˜10-1000 pF RF decouplingcapacitor C3 ˜1.0-22 pF RF tuning and DC block capacitor C4 ˜10-1000 pFRF decoupling capacitor. L1 ˜1.5 to RF tuning and DC bias feed inductor22 nH L2 ˜1.5 to RF tuning and DC bias feed inductor 22 nH R1 0 to 27ohm Lossy resistance to aid stability Q1 RF frequency, high linearityField Effect Transistor (FET), low noise preferred Detector 202 C5 ˜1-22pF Provides DC blocking and RF coupling between the output of RFamplifier 201 and level detector 202. The smaller its value, the lessthe coupling. C6 ˜22-100 pF RF decoupling capacitor D1 Rectificationdiode chosen for desired detector characteristics D2 Rectification diodechosen for desired detector characteristics L3 ˜22-39 nH RF choke BiasConditioner 205 C7 27-1000 pF Capacitor to set the time constant (or thecut off frequency) of the bias control signal U1 Op amp chosen forsignal swing range and response time characteristics R2 ˜1-100K Resistorto set the gain/scaling for ohm the bias level conditioning R3 ˜1-100KResistor to set the gain/scaling for ohm the bias level conditioning notshown Diodes may be optionally used for shaping the input/outputcharacteristic of this stage Variable Resistance 204 Q3 Field effecttransistor (FET) chosen for its characteristic of drain-sourceresistance versus bias R4 ˜51-100K Resistor to scale the variableresistence ohm network R5 10-˜51K Resistor to scale the variableresistence ohm network Bias Generator 203 Q4 Dual PNP bias transistor R6˜2.7 to 10K Sets current on left PNP transistor ohms within Q4, helpsset how much Q1's bias varies with signal strength R7 ˜10 to 100 Sets DCbias through Q1 ohms R8 ˜10 to 100K Aids stability of DC bias networkohms R9 ˜10 to 100K Aids stability of DC bias network ohms

The use of op amp U1 or of any type of active amplification in the biascontrol path, adds cost, complexity and power consumption to thereceiver. Nevertheless, U1 can support several potentially advantageousfeatures of this embodiment of the invention.

One advantage of using an op amp is that relatively precise control canbe obtained over the bias level and the gain, limiting, filtering andhysteresis of its adjustment.

Also, by using an op amp such as U1, feedback can be used to compensatefor variations due to temperature changes or component tolerances. Thisfeedback could be directly from the bias current in the amplificationdevice, such as by sensing the voltage drop across R7.

Another way to obtain such precision is via digitizing the detectedsignal level. The digital signal level can be used as an index into alook-up table, which can contain a precisely calibrated digital biaslevel for each digital signal level. The digital bias level can then beconverted back into an analog bias level.

Another advantage of using an op amp such as U1 is that it provides anamplification element in the bias control path.

One factor that should be considered in the design of a reactivelybiased RF amplifier is that non-linearity in the RF front end of areceiver can have a significant system impact at fundamental peak signallevels that are very small. These peak signal levels may be much smallerthan the bias level of the RF amplifier. U1's amplification of therelatively small detected signal level allows the bias level of the RFamplifier to vary over an appropriate range.

Another factor that plays an important role in the design of reactivelybiased RF amplifiers according to the invention is the measure ofintermodulation known as the IIP³, or the third-order inputintermodulation product. If an amplifier is non-linear, then the energyof the input signal is shifted into harmonics of the frequency of theinput signal. If two signals at different frequencies are present in asignal amplified non-linearly, then these harmonics intermodulate or mixto produce intermodulation products, i.e. multiple frequencies at thesum and difference of all of the frequencies present. If these productsfall within the bandwidth of the signal of interest and have sufficientamplitude, then the usability of the receiver deteriorates. The IIP³ isa measure of the amplitude of these intermodulation products

A receiver's IIP³ can be estimated by one skilled in the art based onits circuit configuration and component values. Also, it can bedetermined via a circuit simulation based on a hypothetical signalenvironment, i.e. the signal strength, frequency and bandwidth of thedesired signal and of any jamming or extraneous signals. Also, it can bemeasured based on the performance of an actual prototype or productionreceiver.

Yet another design factor to be considered is cross talk, i.e. where thetransmitted signal from a transceiver enters its received signal pathand becomes part of the receiver's signal environment. The designdetails of how to reduce the adverse affects of cross talk withappropriate filtering will be easily determined by one skilled in theart, where the filtering is between the transmitter section and thereceiver, within the receiver section, or both.

Nevertheless, cross talk can interact with intermodulation. Thisinteraction can be difficult to predict via static calculations. Theseinteractions can be examined by one skilled in the art, by means ofdynamic simulation of the circuit design using realistic models ofsignal environments, perhaps based on target specifications forintermodulation rejection. They can also be examined by experimentaltesting of bread boards of the circuit design and of prototypetransceivers or production transceivers. Because reactively biasedamplifiers dynamically vary their intermodulation rejection, suchsimulations and testing can play an important role in determining howmuch to vary the bias level in different signal environments.

Another design factor to be considered is that the target specificationspublished for receivers do not take into account the effects of reactivebiasing. Published specifications may assume that a high-noiseenvironment is the worst case for a receiver; thus, they may onlyspecify target intermodulation parameters under such conditions. Areactively biased receiver could operate well under the published testconditions because it detects the strong signal environment and ups itsbias levels accordingly. However, it is possible for that same receiverto have problems in the presence of intermediate levels of jammingsignals (or even under low levels of jamming signals) if it is tooaggressive about lowering its bias levels under such conditions.

Thus, a reactively biased receiver should be designed for and testedover the entire range from high levels of jamming signals to minimal ornon-existant jamming signals.

Another design factor to be considered is a possible effect on the gainof the amplifier when its bias level is reactively adjusted. It may bedesirable to select the range of bias level and other characteristics ofthe amplifier such that there is little if any change in its gain as itis reactively biased. One benefit of such an approach is that it may bedesirable to keep the amplifier operating at or near maximum gain,particularly if the amplifier is early in the front end of the receiverwhere the signal strengths are low.

Another benefit of this approach is that it minimizes the possibility ofa positive feedback loop with respect to the receiver's gain. The gainfeedback loop arises as follows: a stronger signal level being detectedincreases both the bias level and the gain of the amplifier, then astill stronger signal level will be detected, which will again increasethe bias level and again increase the gain, etc. If such a change ingain of 1 dB (for example) results in a subsequent change in gain ofsubstantially less than 1 dB, then this feedback effect will stabilize.In this case, this feedback effect can have a desirable effect on theshape of the transfer function over the bias range—for example, it mayreduce or eliminate the need to amplify or condition the bias controlsignal.

On the other hand, if a change in gain of 1 dB (for example) results ina subsequent change in gain near, or more than 1 dB, then this feedbackeffect will not stabilize. Thus, the reactive biasing and perhaps thereceiver itself will not operate properly.

FIG. 3 is a circuit diagram of a simplified RF amplifier, according toone embodiment of the invention. This circuit avoids the costs,complexity and power consumption of the op amp of the circuit of FIG.2A. This is a significant reduction. In terms of circuit area for animplementation on a monolithic integrated circuit and in terms of powerconsumption, U1's area and power requirements might be on the order ofthose of all of the rest of FIG. 2A's circuitry put together.

This embodiment also blurs the distinctions among the functional blocksshown in FIGS. 1 and 2 in that several of this circuit's componentsaffect how the circuit functions in multiple ways that cross theboundaries of these functional blocks.

The components of the self-adjusting, reactively biased RF amplifier ofFIG. 3, their suitable values and their functional description are givenby the following table:

TABLE 2 Components of Simplified, Reactively Biased RF AmplifierReference Suitable Designator Value Function C1 ˜0.1 uF Helps set thetime constant of the detector circuit. Also provides RF decoupling. C2˜22 pF Provides RF bypass to prevent RF feedback C3 ˜22 pF Optional.Provides RF bypass at the source of Q1. C4 ˜22 pF Provides DC blockingand impedance matching for the detector circuit C5 ˜2-22 pF Provides DCblocking and impedance matching for the input of the amplifier C6 ˜2-22pF Provides DC blocking and impedance matching for the output of theamplifier C7 ˜22 pF Provides RF bypass at the emitter of Q2 D1 SchottkeyRectification diode for the detector circuit D2 Schottkey Voltagedoubler diode and return path pair for the detector current L1 ˜6.8 nHRF choke and load matching inductor L2 ˜4.7 nH Output matching inductorR2 ˜1K ohms Sets bias of the detector circuit R3 ˜5K ohms Sets timeconstant and bias voltage of the detector circuit R4 ˜30K ohms Optional.Scales the bias level R5 ˜50K ohms Sets bias feedback for Q1. Also aidsin conditioning the bias control. Also helps set the bias level. R610-20K Operates with R7 to set bias feedback for Q2 ohms R7 ˜10K ohmsSets feedback for both Q1 and Q2. Also helps set the bias level. R8 ˜10ohms Part of bias feedback for Q1. Also helps set the collector bias forQ2 R9 ˜140 ohm Scales the variable resistence of Q1 R10 0-˜10 ohmsOptional. Sets collector bias of Q2 without providing feedback on Q1 R110-˜20 ohms Optional. Provides Q2 emitter stabilization resistance Q1N-channel Biasing transistor configured to form a variable power FETresistance circuit Q2 Bipolar RF Amplifying transistor transistor

One factor that should be taken into consideration in the design of areactively biased RF amplifier according to the invention is that thenon-linearity in the RF or front end of a receiver can have asignificant system impact at fundamental peak signal levels much smallerthan the bias level of the RF amplifier. Therefore, it is desirable thatthe detector be able to sense a small signal and apply enough biascontrol to accommodate this signal condition. One way this can be doneis for matching elements to be added at the detector's input, which arecoordinated with the matching elements at the amplifier's output. Whilethis can be an effective technique in some situations, activeamplification along the lines of the previous figure may be required insome low-noise or small-signal applications.

FIG. 4 is a circuit diagram of a self-adjusting, reactively biasedintermediate frequency (IF) amplifier according to one embodiment of theinvention. Its components, their preferred values and their functionaldescriptions are given by the following table:

TABLE 3 Components of Reactively Biased IF Amplifier Reference SuitableDesignator Value Function C1 ˜0.1 uF Sets the time constant of thedetector circuit C2 ˜100 pF Provides IF bypass to prevent IF feedback C3˜100 pF Optional. Provides IF bypass at the source of Q1. C4 ˜100 pFProvides DC blocking and impedance matching for the detector. However,without C4, the DC present could be used to bias the detector. C5 ˜2-22pF Provides DC blocking and impedance matching for the input of theamplifier C6 ˜2-22 pF Provides DC blocking and impedance matching forthe output of the amplifier C7 ˜100 pF Provides IF bypass at the emitterof Q2 D1 Schottkey Rectification diode for the detector circuit D2Schottkey Optional. Accelerates the response of pair the system tochanges in signal conditions at the high end L1 ˜560 nH IF choke andload matching inductor L2 ˜330 nH Output matching inductor L3 22-39 nhRF choke R0 ˜30K ohms Optional. Establishes an active bias for thedetector circuit, which may or may not be desired R1 ˜100K ohmsOptional. Scales the IF input to the detector R2 ˜30K ohms Optional.Scales the IF input to the detector R3 ˜5k ohms Optional. Establishes aDC return path and sets a leakage bias for the detector R4 ˜30k ohmsOptional. Scales the bias level R5 ˜50K ohms Sets bias feedback for Q1and sets the time constant of the detector R6 ˜10-20K Operates with R7to set bias feedback for Q2 ohms R7 ˜10K ohms Sets feedback for both Q1and Q2 R8 ˜10 ohms Part of bias feedback for Q1. Also helps setcollector bias for Q2 R9 ˜140 ohm Scales variable resistence of Q1 R100-˜10 ohms Optional. Sets collector bias of Q2 without providingfeedback on Q1 R11 0-˜20 ohms Optional. Provides Q2 emitterstabilization resistance Q1 N-channel Biasing transistor configured toform a power FET variable resistance circuit Q2 Bipolar IF IF amplifyingtransistor transistor

In an alternative embodiment of a reactively biased IF amplifieraccording to the invention, R0 could provide the detector bias.

One factor that should be taken into consideration in the design of areactively biased IF amplifier according to the invention is that itslinearity requirement may not be as great as for a front-end RFamplifier; that is, a substantially stronger jamming signal may berequired at IF stages to produce undesirable amounts of intermodulation.Therefore, the relative range of adjustment in the bias levelappropriate for an IF amplifier may be smaller than for an RF amplifier.

Another factor that should be taken into consideration in the design ofa reactively biased IF amplifier according to the invention is that thesignal strength of its output may be substantially higher than for an RFstage. Therefore, it may be possible for its output signal to be scaled,rectified and the resulting signal scaled again. This can allow the IFamplifier to be self-adjusting according to the transfer functiondesired. In contrast, the relatively weak signals at the RF level maynot allow such two-stage scaling.

FIG. 5 shows the application of one embodiment of the invention in atransceiver application, such as but not limited to a mobile phonedevice or a two-way pager. In transmitter section 550, final poweramplifier 503 provides an RF transmission signal to antenna 501, viaantenna signal line 521 and duplexer 502. Duplexer 502 can be a filter,or set of filters, that allows the RF energy output of final poweramplifier 503 to be coupled to antenna 501 while filtering this energyto reduce the amount of it that enters the receiver section of thedevice.

FIG. 5 is also a functional block diagram of the front end of areceiver, according to one embodiment of the invention, with multiplestages of amplification, each stage having self-adjusting reactivebiasing. Receiver section 551 receives RF input signal 523 from antenna501 via duplexer 502. It produces IF output signal 533. As shown, it hasfour stages of active circuitry, each with self adjusting bias; however,other embodiments can have more or fewer active circuit stages. Also inyet other embodiments, some of the active circuits can have a fixedrather than self adjusting bias, or commonly controlled bias levels

Receiver section 551 is not a complete receiver; however, the designdetails of other circuitry required for a specific application of theinvention will be easily determined by one skilled in the art. It mayinclude but not be limited to a local oscillator, local oscillatorbuffer, IF to audio/digital converter, audio/digitalamplification/processing, automatic gain control, user interface, andaudio/video input/output.

Initial low-noise amplifier 504 receives RF input signal 523 andproduces internal RF signal 525. The bias of initial low-noise amplifier504 can be set by first self-adjusting bias level 524, which can beproduced internally to initial low-noise amplifier 504 (as shown) or canbe produced based on internal RF signal 525.

Initial low-noise amplifier 504 can be any type of RF amplifier withcharacteristics suitable for the particular application. In particular,initial low-noise amplifier 504 can be the RF amplifier shown in FIG.2A, or a variation thereof. Bias adjustment circuit 205, which includesop-amp Q2, allows this amplifier stage to re-actively bias according tochanges in the relatively low signal levels at the initial RF stage of areceiver. That is, relatively small changes in RF signal levels of RFinput signal 523 can be amplified by op-amp Q2 to produce adjustments infirst self-adjusting bias level 524 that are large enough that thelinearity/intermodulation rejection of initial low-noise amplifier 504can be preserved in high-signal environments.

Filter 505 receives internal RF signal 525 and produces internal RFsignal 526. Filter 505 can attenuate out of band components within theRF signal, including but not limited to any leakage (through duplexer502) of transmission energy into the receiver section.

Second RF amplifier 506 receives internal RF signal 526 and producesinternal RF signal 528. The bias of second RF amplifier 506 can be setby second self-adjusting bias level 527, which can be producedinternally to second RF amplifier 506 as shown or which can be producedbased on internal RF signal 526 or 528.

Second RF amplifier 506 can be any type of RF amplifier withcharacteristics suitable for the particular application. In particular,second RF amplifier 506 can be the RF amplifier shown in FIG. 3, or avariation thereof. While the bias adjustment conditioning function inthis receiver does not include an op-amp, the position of this amplifieras the second stage within the receiver gives this amplifier stage ahigher signal level to work with. Therefore, this second RF stage may besensitive enough to appropriately adjust its bias without the addedcost, complexity and power consumption of an op-amp.

RF to IF converter 507 receives internal RF signal 528 and producesinternal IF signal 530. The bias of RF to IF converter 507 can be set bythird self-adjusting bias level 529, which can be produced internally toRF to IF converter 507 as shown or which can be produced based oninternal RF signal 528 or internal IF signal 530.

RF to IF converter 507 can be any type of RF to IF converter or mixerwith characteristics suitable for the particular application.

IF amplifier 508 receives internal IF signal 530 and produces internalIF signal 532. The bias of IF amplifier 508 can be set by fourthself-adjusting bias level 531, which can be produced internally to IFamplifier 508 or which can be produced based on internal RF signal 530or internal IF signal 532.

IF amplifier 508 can be any type of IF amplifier with characteristicssuitable for the particular application. In particular, IF amplifier 508can be the IF amplifier shown in FIG. 4, or a variation thereof. This IFstage may be sensitive enough to appropriately adjust its bias withoutthe added cost, complexity and power consumption of an op-amp.

Filter 509 receives internal IF signal 532 and produces IF output signal533. Filter 509 can attenuate out of band components within the signal.

As shown, each active stage in receiver section 551 has its own selfadjusting bias level. Substantial reductions in the use of receiverpower in some signal environments can be achieved by the embodiment ofthe invention shown in FIG. 5. For example, to the extent that energyfrom jamming sources (including but not limited to energy leaked fromfinal power amplifier 503 via duplexer 502) is attenuated by filteringbetween active stages, then stages after the filtering can operate atreduced bias levels and at reduced power consumption relative to thestages prior to the filtering. Nevertheless, some of the active stageswithin receiver section 551 could be implemented with fixed bias levels,or with bias levels subject to a common control.

FIG. 6 is a functional block diagram of a receiver front end, accordingto one embodiment of the invention, with multi-stage reactive biasingthat has a common control. It differs from the embodiment of theprevious figure in that all active stages with reactive biasing operateat the same relative bias level depending on the strength of the currentsignal environment. It also differs from the previous figure in that thebias level of local oscillator & buffer 608 is adjusted in reaction tosignal level.

FIG. 6 is a functional block diagram of receiver front end 600. Receiverfront end 600 receives RF input signal 631 from antenna 601 and producesIF output signal 635. As shown, it has five stages of active circuitry,each with reactively adjusted bias. However, other embodiments can havemore or fewer active circuit stages, or some of the active circuits canhave a fixed rather than a reactively adjusted bias, or some of theactive circuits can have a self adjusting bias.

Receiver front end 600 is not a complete receiver; however, the designdetails of other circuitry required for a specific application of theinvention will be easily determined by one skilled in the art. It mayinclude but not be limited to an IF to audio/digital converter,audio/digital amplification/processing, automatic gain control, userinterface, and audio input/output.

First RF amplifier 602 amplifies RF input signal 631 into internal RFsignal 632. The bias of first RF amplifier 602 can be set by bias level642, which can be produced by first bias generator 612. First RFamplifier 602 can be any type of RF amplifier with characteristicssuitable for the particular application. For example, it can be RFamplifier 201 as shown in FIG. 2A.

Second RF amplifier 603 amplifies internal RF signal 632 (which can bedirectly as generated by first RF amplifier 602 or after suitablefiltering) into internal RF signal 633. The bias of second RF amplifier603 can be set by bias level 643, which can be produced by second biasgenerator 613. Second RF amplifier 603 can be any type of RF amplifierwith characteristics suitable for the particular application. Forexample, it can be the RF amplifier shown in FIG. 3.

RF to IF converter 604 converts internal RF signal 633 into internal IFsignal 634. RF to IF converter 602 can be any type of RF to IF converteror mixer with characteristics suitable for the particular application.

IF frequency signal 654 can be produced by local oscillator & buffer624. The bias used in local oscillator & buffer 624 can vary in reactionto the strength of the signal environment in which the receiver iscurrently operating. The bias level used by local oscillator & buffer624 can be bias level 644, which can be generated by third biasgenerator 614.

Local oscillator & buffer 624 can be any type of an oscillator and/orbuffer that can produce IF frequency signal 654. In some embodiments,the local oscillator portion produces a signal at the chosen IFfrequency, and the active stage that amplifies and/or buffers this IFsignal prior to its use in RF to IF converter 604 can use adjustablebias level 644.

Such reactive biasing of the local oscillator & buffer is like thereactive biasing of the RF and IF amplification stages in that it isdone in order to save power in typical signal environments, i.e., thosein which the extraneous or jamming signals are not as strong as they areunder worst-case operating conditions. However, such reactive biasingdiffers from that of the amplifier stages in that it operates by varyingthe compression point and perhaps the gain of local oscillator 624, orof the buffer/amplifier stage within local oscillator 624. The designdetails of local oscillator and buffer 608 will be readily determined byone skilled in the art. In contrast to reactively biased amplificationstages, it may be preferable to choose a bias level range and otherparameters for local oscillator and buffer 624 such that any change ingain is low or minimal.

IF amplifier 605 amplifies internal IF signal 634 into IF output signal635. The bias of IF amplifier 605 can be set by bias level 645, whichcan be produced by fourth bias generator 615. IF amplifier 605 can beany type of IF amplifier with characteristics suitable for theparticular application. For example, it can be the IF amplifier shown inFIG. 4.

As shown in FIG. 6, level detector 606 receives IF output signal 625. Itdetects the signal level of IF output signal 625, and thus indirectly itdetects the signal level of RF input signal 631. In other embodiments,level detector 606 can receives a signal that is intermediate between RFinput signal 631 and IF output signal 635. According to this signal level, level detector 606 produces bias control signal 636.

Level detector 606 can be any type of circuit that is able to detectchanges in the average input and output signal levels that occur over asuitable time frame. In particular, it can be level detector 202 asshown in FIG. 2A with suitable modifications to adapt the circuit to IFfrequencies.

Bias adjustment circuit 607 produces adjusted bias control signal 637according to bias control signal 636. Bias adjustment circuit 607 can beany circuit that is able to adjust bias control signal 637 in a mannerthat matches the response of level detector 605 to the bias variationrequired by the active stages whose bias is being reactively controlled.

For example, bias adjustment circuit 607 can be bias conditioner 205 asshown in FIG. 2A. As other examples, bias adjustment circuit can includecircuitry that conditions bias control signal 636, scales it, comparesit against a reference level, samples and holds it, sums a held levelwith a variable level, or any combination of these. It can also includecircuitry that monitors feedback on the actual level of one or more ofthe reactive bias levels so as to provide improved control over bias.

Bias adjustment circuit 603 can also include circuitry that compensatesfor threshold variations of active devices with the reactive biasingsystem, including but not limited to variations in the threshold of itsfield effect transistors (FETs). Because the linear range of a FET maybe narrow, it may be important to calibrate or set the levels used so asto maintain the circuit's operation within that linear range.

Alternatively, bias adjustment circuit 607 can be eliminated orsimplified. This can apply if level detector 606 has a relatively strongsignal (such as an IF signal) to work with and is thus able to produce abias control signal of a suitable level and range of variation for biasgenerators 612 through 616 to work with directly.

First bias generator 612 can produce first bias level 632 according toadjusted bias control signal 627 and, optionally, according to a firstregulating feedback signal that is internal to first bias generator 612.Similarly, second bias generator 613 can produce second bias level 633according to adjusted bias control signal 627 and, optionally, a secondregulating feedback signal that is internal to second bias generator613. Similar principles apply to bias generators 614 through 615.

Bias generators 612 through 615 can be any circuits that are able toproduce a bias level that varies within a suitable range according toadjusted bias control signal 637 or bias control signal 636. Asexamples, they can be (as shown in FIG. 2A) bias generator 203 usingvariable resistance 204-A, 204-B or 204-C.

In other embodiments of the invention each bias generator can have acorresponding bias adjustment circuit. Alternatively, two or more biasgenerators could operate from a first bias adjustment circuit and otherbias generators can have one or more other bias adjustment circuit orcan directly use bias control signal 636 and thus not need a biasadjustment circuit.

The series of commonly controlled reactively biased amplifiers as shownin FIG. 6 can provide substantial reductions in the use of receiverpower in some signal environments. It has fewer components and thus lessmanufacturing costs, compared with the self-adjusting amplifier stagesshown in the previous figure, It has less complexity, and thus is easierto test and less prone to failure. Its only level detector is locatedafter multiple stages of amplification, thus its bias conditioner maynot need to include active amplification because it has a relativelystrong signal to work with. Also, it may consume less power because ofonly having one level detector 606, only having one bias adjustmentcircuit 607 or not requiring amplification to condition the bias controlsignal.

The amplifier of FIG. 6 may be appropriate where RF or other earlyfiltering is not effective to attenuate jamming signals. This amplifiermay also be appropriate for applications where it is undesirable to addthe cost, complexity and power consumption of making each stage selfadjusting—that is, of having each amplification stage have its owndedicated level detector and perhaps its own dedicated bias adjustmentcircuit.

One skilled in the art will be easily able to determine the designdetails of a receiver that is a hybrid of the self-adjusting stages ofFIG. 5 and the commonly controlled stages of FIG. 6. For example, onebias control signal could be used for two or more amplifier or otheractive stages while self-adjusting bias control could be used for otheractive stages. Further, such a multi-stage receiver could also includeactive stages with fixed bias levels.

FIG. 7 is a functional block diagram, according to one embodiment of theinvention, of receiver front end 700 in which both a filter and an RFamplifier are optionally included in the receiver's signal path orswitched out of it. Receiver front end 700 receives RF input signal 720and produces IF output signal 732.

As shown, receiver front end 700 has two stages of active circuitry,each with a reactively adjusted bias under common control, and oneswitch. However, other embodiments can have more switches, more or feweractive circuit stages, or some of the active circuits can have a fixedrather than a reactively adjusted bias, or some of the active circuitscan have a self adjusting bias.

Low noise amplifier 701 amplifies RF input signal 720 into firstinternal RF signal 721. The bias of low noise amplifier 701 can be setby first bias level 729, which can be produced by first bias generator709. Low noise amplifier 701 can be any type of RF amplifier withcharacteristics suitable for the particular application. For example, itcan be RF amplifier 201 as shown in FIG. 2A.

RF switch and bypass circuit 702 receives first internal RF signal 721and produces switched RF signal 725. When in bypass mode, i.e. whenbypass control signal 731 is asserted, switched RF signal 725 issubstantially first internal RF signal 721, though some switching lossmay occur within RF switch and bypass circuit 702. When bypass controlsignal 731 is not asserted, switched RF signal 725 can be the result offiltering first internal RF signal 721 by first filter 703 andamplifying the result by RF amplifier 704. Alternatively, switched RFsignal 725 can be the result of amplifying first internal RF signal 721by RF amplifier 704 and filtering the result by first filter 703.

RF switch and bypass circuit 702 can be any circuit able to transfereither first internal RF signal 721 or fourth internal RF signal 724 toswitched RF signal 725. Further, it is preferably a circuit able totransfer first internal RF signal 721 to either second internal RFsignal 722 or to switched RF signal 725 but not to both, so as to notunnecessarily load first internal RF signal 721 when operating in bypassmode.

First filter 703 receives second internal RF signal 722 from RF switchand bypass circuit 702 and produces third internal RF signal 723. Firstfilter 703 can be any circuit able to reduce undesired or jammingcomponents of second RF signal 722. In some embodiments, receiver frontend 700 is used in a transceiver device and first filter 703 is atransmission blocking filter.

RF amplifier 704 amplifies third internal RF signal 723 into fourthinternal RF signal 724. The bias of second RF amplifier 704 can be setby second bias level 730, which can be produced by second bias generator710. Second RF amplifier 704 can be any type of RF amplifier withcharacteristics suitable for the particular application. For example, itcan be the RF amplifier shown in FIG. 3.

In some embodiments of the invention, second filter 705 receivesswitched RF signal 725 from RF switch and bypass circuit 702 andproduces fifth internal RF signal 726. In other embodiments, there is nosecond filter and switched RF signal 725 is directly provided to RF toIF converter 706 and level detector 707. Second filter 705 can be anycircuit able to reduce undesired or jamming components of switched RFsignal 724. In some embodiments, receiver front end 700 is used in atransceiver device and second filter 705 is a transmission blockingfilter.

RF to IF converter 706.converts fifth internal RF signal 726, orswitched RF signal 725, into internal IF output signal 732. RF to IFconverter 726 can be any type of RF to IF converter or mixer withcharacteristics suitable for the particular application.

As shown in FIG. 7, level detector 707 receives fifth internal RF signal726, or switched RF signal 725. It detects the signal level of thissignal, and thus indirectly it detects the signal level of RF inputsignal 720. In other embodiments, level detector 707 can receive asignal that is intermediate between RF input signal 720 and switched RFsignal 725, it can receive IF output signal 732, and/or it canoptionally receive a second IF output signal 752 after the IF outputsignal 732 is filtered through an IF filter 750 to produce the second IFoutput signal 752. According to this signal level, level detector 707produces bias control signal 727 and bypass control signal 731.

Level detector 707 can be any type of circuit that is able to detectchanges in the average input and output signal levels that occur over asuitable time frame. In particular, bias control signal 727 can begenerated by level detector 202 as shown in FIG. 2A, and bypass controlsignal 731 can be generated by comparing bias control signal 727 againsta threshold.

Bias adjustment circuit 708 produces adjusted bias control signal 728according to bias control signal 727. Bias adjustment circuit 708 can beany circuit that is able to adjust bias control signal 637 in a mannerthat matches the response of level detector 707 to the bias variationrequired by the active stages whose bias is being reactively controlled.

For example, bias adjustment circuit 708 can be bias conditioner 205 asshown in FIG. 2A. As other examples, bias adjustment circuit can includecircuitry that conditions bias control signal 727, scales it, comparesit against a reference level, samples and holds it, sums a level heldwith a variable level, or any combination of these. It can also includecircuitry that monitors feedback on the actual level of one or more ofthe reactive bias levels so as to provide improved control over bias.

Bias adjustment circuit 708 can also include circuitry that compensatesfor threshold variations of active devices within the reactive biasingsystem, including but not limited to variations in the threshold of itsfield effect transistors (FETs). Because the linear range of a FET maybe narrow, it may be important to calibrate or set the levels used so asto maintain the circuit's operation within that linear range.

Alternatively, bias adjustment circuit 708 can be eliminated orsimplified. This can apply if level detector 707 has a relatively strongsignal (such as an IF signal) to work with and is thus able to produce abias control signal of a suitable level and range of variation for biasgenerators 709 and 710 to work with directly.

First bias generator 709 can produce first bias level 729 according toadjusted bias control signal 728 and, optionally, according to a firstregulating feedback signal that is internal to first bias generator 709.Similarly, second bias generator 710 can produce second bias level 730according to adjusted bias control signal 728 and, optionally, a secondregulating feedback signal that is internal to second bias generator710.

Bias generators 709 and 710 can be any circuits that are able to producea bias level that varies within a suitable range according to adjustedbias control signal 728 or bias control signal 727. As examples, theycan be (as shown in FIG. 2A) bias generator 203 using variableresistance 204-A, 204-B or 204-C.

In other embodiments of the invention each bias generator can have acorresponding bias adjustment circuit.

Code division multiple access (CDMA) receivers can include a receiverchain that includes a low-noise amplifier (LNA) that can be bypassed bya switch, followed by a transmission rejection filter, followed by an RFamplifier that can be bypassed by a switch.

In cellular phone applications, it is important that the volume levelthe user perceives not vary with signal strength. To meet this need, thegain of the receiver chain, and sometimes the gain of the subsequentdemodulation and audio amplification, can be relatively preciselycalibrated by digitizing a signal that represents the current signalstrength into an 8-bit signal strength value representing, for example,signal strengths ranging from −106 to −21 dBm. This signal strengthvalue can be used as an index into a lookup table, each entry of whichrepresents a calibration factor that is used to control the gain. Such alookup table apparatus is called a “linearizer” because it corrects forthe non-linearity of the automatic gain control (AGC) level versus thereceived signal strength level.

When one of the amplifiers in the receiver chain is bypassed, thelinearizer curve should be shifted by the change in gain due tobypassing the amplifier. To continue with the above example, bypassingan amplifier results in the low end of the linearizer curve shiftingfrom −106 dBm to −106 plus the change in gain.

This change in gain can be estimated as follows: Each amplifier can havea gain of, for example, 15 to 16 dB. There can be some loss in thebypass path, for example 0.5 dB or more. Also, there is typically 1 dBuncertainty in the calibration process, which should be added here asmargin. This results in the end of linearizer curve being−106+15.5+0.5+1=−89 dBm.

A proposed extended jamming signal test calls for a desired signalhaving a strength of −90 dBm that is concurrent with a two-tone jammingsignal having a signal strength of −32 dBm for each tone.

This test can present a problem for the receiver if it is unable tooperate with one of the amplifiers bypassed. Specifically, the linearityor IIP³ of the RF amplifier must be significantly higher than if the RFamplifier is bypassed at the operating point (i.e. signal strength)corresponding to this test.

Qualitatively, not only does the second amplifier contribute its ownnon-linearity to the chain, it amplifies the undesirable effects of thenon-linearity of the first amplifier. Quantitatively, this difference inIIP³ can be required can be roughly estimated as equivalent to the gainthat could be bypassed.

However, bypassing either the LNA or the RF amplifier can present aproblem if the operating point of interest falls off the linearizer;that is, if there is no entry in the look-up table for the correspondingdigital strength value.

A first approach to dealing with this problem of is to automatically putback in the gain, i.e. switch back in the amplifier. This raises thereceived signal back into the range where the linearizer can compensatefor non-linearity at the operating point of interest. This approachprevents the receiver from operating with either of its amplificationstages bypassed when such operation would result in the digitized signalstrength being below the end of the linearizer table.

A drawback of this first approach is that having both amplifiersswitched in can significantly increase the linearity requirement thatthe second amplifier must meet, as discussed above.

A second approach is to move the transmission rejection filter into thebypass path. Using this architecture, the point at which one of theamplifiers is switched in and out, i.e. the bypass point, can be loweredto the insertion loss of this filter, which can be about 2 dB, forexample. This can allow the bypass point to be about −91 dBm. Such abypass point can be less than the −90 dBm extended jamming signal testdescribed above.

Using the second approach can facilitate the goal of switching out oneof the amplifiers for this test. That is, bypassing the filter allowsthe IIP³ of the second stage amplifier to be significantly lower.

Another advantage of the second approach, and of the lower bypass pointthat it enables, is that in actual operation of the receiver one of theamplifiers is likely to be bypassed for a greater portion of theoperating time. The power consumed by the amplifier can be reduced oreliminated when it is unused. This can further save power and prolongbattery life.

TABLE 4 Breakdown of IS-95 J-STD-018 CDMA RX inter-modulationperformance specs input CDMA level (dBm) input tone level (dBm) # oftones −101 −30 1 −101 −43 2 −90 −32 2 −79 −21 2

In the following table, the RF amplifier state is decided upon the CDMAsignal level being above or below the switch point. Case 1 is a switchpoint less than −90, Case 5 is a switch point greater than −90 dBm.

TABLE 5 Breakdown of IS-95 J-STD-018 CDMA RX inter-modulationperformance specs input CDMA level input tone level Case (dBM) (dBm) RFAmp State 1 −90 −32 bypassed 2 −101 −43 engaged 3 −79 −21 bypassed 4−101 −30 engaged 5 −90 −32 engaged

The following table is generated by considering the input level uponeach device given. 3 dB insertion loss and 50 dB transmission rejectionwas used for the duplexer. 2 dB insertion loss and 25 dB transmissionrejection was used for the transmission rejection filter. IIP³ can becalculated by the well known formula IIP³=½(3*Tone level−Intermodulationproduct level). IIP³'s were calculated for an intermodulation productlevel marginally acceptable for demodulation of the CDMA signal. IIP³for cross-modulation with the transmission leakage and a single-tone isa phenomena best predicted by measurement and simulation. In some casesboth inter-modulation and cross-modulation contribute to raise therequired IIP³ greater than one type alone. Gain used for the LNA was 16dB, 15 dB for the RF amplifier, and 1 dB loss for the switches. Detectorlevels are increased by 3 dB in the cases of two equal level jammingtones contributing.

TABLE 6 Linearity requirements for each of the stages vs cases anddetector level (all levels dBm) Case LNA IIP3 RF Amp IIP3 Mixer IIP3Detector level 1 −4.5 Bypassed 10.5 −15.5 2 1.5 −2.7 12.3 −13.2 3 3.5Bypassed 18.5 −6 4 8.0 −1.0 14.0 −3.9 5 −4.5   6.5 21.5 −3.0

It is evident that not bypassing the RF amplifier in Case 5 creates amuch higher demand for IIP³ from the RF amplifier and the mixer. Thesecond highest demand for the mixer comes from Case 3 in whichcross-modulation from the transmitter plays no part, which shows therewas no performance degradation due to having the transmission rejectfilter in the bypass path.

FIG. 8 is a circuit diagram for an embodiment of the invention that usesa sample and hold circuit to improve the accuracy and effectiveness ofthe reactive bias function by compensating for variations of circuitcomponents, operating conditions or both. These variations include butare not limited to variations in the thresholds of the field effecttransistors (FETs) used. The range of linear operation of a FET can benarrow and its threshold voltage (and thus the point at which it doesoperate linearly) can be affected by manufacturing tolerances,temperature variations or voltage fluctuations. Thus, it can beadvantageous to dynamically compensate for such variations, particularlywhen done as the same time as dynamically compensating for the signalstrength of the receiver's current operating environment.

In the example circuit diagram of FIG. 8, RF amplifier 801 can beequivalent or identical to RF amplifier 201 as shown in FIG. 2A.Detector 802 can be a minor variation (i.e. adding R20) from detector202 as shown in the same figure.

The function of bias generator 803 is similar to that of bias generator203 as shown in the same figure, but it alters the bias of RF amplifier201 by changing the bias current level, while the bias voltage levelremains substantially constant. To implement this, the variableresistance circuit within bias generator 803 is moved to the bottomportion of bias generator 803. Another difference is that in biasgenerator 803 when shutdown signal 851 is asserted, all bias voltage andcurrent is shut off to RF amplifier 801.

These variations between bias generator 203 and 803 are independent ofthe threshold compensation feature of receiver 800; a thresholdcompensating receiver could be designed using bias generator 203 or arange of similar circuits.

The bias adjustment function is performed by bias level comparitor 810,sample and hold circuit 811 and bias difference circuit 812.

Bias level comparitor 810 can be any type of circuit that is able togenerate regulating feedback signal 842. In particular, regulatingfeedback signal 842 can be generated by comparing a reference voltageagainst a signal internal to bias generator 803. In the embodimentshown, the reference voltage is formed by a two resistor voltage dividerbetween Vcc and ground, which helps compensate for variations in Vcc.

Sample and hold circuit 811 can be any type of circuit that is able tosample regulating feedback signal 842 when the signal environment inwhich the receiver is sufficiently quiescent, and hold that signal valuewhen the signal environment is stronger. In the embodiment shown, whenbias control signal 840 is below a threshold set by detector referencesignal 850 then the current value of regulating feedback signal 842 issampled or transferred onto capacitor C20, and when above then the valueis held on C20.

Bias difference circuit can be any type of circuit that appropriatelyadjusts bias control signal 840 into adjusted bias control value 841.The adjustments can include but are not limited to generating thedifference between bias control signal 840 and the value being sampledvia capacitor C20 or held on capacitor C20.

FIG. 9 is a circuit diagram and an pin out diagram of an applicationspecific integrated circuit (ASIC) for bias control according to oneembodiment of the invention. As shown, many of the electronic circuitcomponents of FIG. 8 are formed within a single integrated circuithaving 10 pins. Implementing these circuit components as an ASIC canreduce manufacturing costs and complexity of receivers that usereactively biased front end circuits.

It will be obvious to one skilled in the art that there are numerousother selections of what circuit components within FIG. 8, or withinanother embodiment of the invention, can be integrated. For example, an8 pin embodiment can be designed that omits the Bias Adjustment andShutdown signal pins.

FIG. 10 shows the functional components and their interconnections foranother embodiment of the invention. This embodiment is the first stagesof a receiver that uses the integrated circuit of the previous figure tobuild a receiver that can be operated in several modes used in mobiletelephone applications. These modes include analog modes such ascellular and advanced mobile phone service (AMPS) as well as digitalmodes such as code division multiple access (CDMA) and personalcommunication service (PCS).

Reactively biased front end circuits according to the present inventioncan be used within various types of mobile telephone receivers, as canswitching in and out the transmission rejection filter when the secondstage RF amplifier is switched in and out.

In the example shown in FIG. 10, antenna 1001 provides, via diplexer1002, an RF signal to both PCS duplexer 1003 and cellular duplexer 1004.PCS duplexer 1003 and cellular duplexer 1004 respectively provide RFsignals to PCS low noise amplifier (LNA) 1005 and cellular LNA 1006.They in turn respectively provide RF signals to optional transmissionrejection filters 1007 a and 1007 b, which in turn provide RF signals toswitch SW1.

SW1 determines whether the RF signal currently of interest (e.g. PCS orcellular) passes through transmission rejection filter 1007 c and secondstage RF amplifier 1008 prior to going on to switch SW 2. Transmissionrejection filter 1007 c, which is optional, is a dual band filter, inthat its filtering applies to both cellular and PCS signals.

Switch SW2, in conjunction with SW1, selects the signal of interest andpasses it on to RF to IF converter 1009. Local oscillator 1010 providesthe intermediate frequency signal to RF to IF converter 1009.

Switch SW3 routes the output of RF to IF converter 1003 on either toAMPS SAW filter 1011 or toCDMA SAW filter 1012

Local oscillator rejection filter 1013 attenuates the local oscillatorsignal from entering level detector 1014. Level detector 1014 producesdetect and hold signal 1041. Bias ASICs 1015 to 1017 use detect and holdsignal 1041 to generate the bias levels for their respective activecircuits.

The bias of PCS low noise amplifier 1005 and of cellular amplifier 1006is reactively set by bias ASIC 1011 according to detect and hold signal1041. The bias of second stage RF amplifier 1008 is reactively set bybias ASIC 1016 according to detect and hold signal 1041. Similarly, thebias of local oscillator 1010 is reactively set by bias ASIC 1017according to detect and hold signal 1041.

One skilled in the art will be easily able to determine how stages andcircuits within the front end of a receiver other than those expresslydiscussed herein could be designed with reactive biasing in accordancewith the principles, spirit and scope of the invention.

As illustrated herein, the invention provides a novel and advantageousmethod and apparatus for the front-end stages of a receiver withreactively biased amplification, oscillation and other circuits toprovide low power, high linearity and low intermodulation. One skilledin the art will recognize that one may employ various embodiments of theinvention, alternative designs for the invention and changes in its formand detail. In particular, the circuits shown in FIGS. 2, 3, 4, 8 and 9may be simplified, augmented or changed in various embodiments of theinvention. Also, the amplifiers of FIGS. 5, 6, 7 and 10 may beintermixed, extended to more stages, simplified, augmented or changed.

Such changes and other changes do not depart from the principles orspirit of the invention, the scope of which is set forth in thefollowing claims.

What is claimed is:
 1. A radio frequency receiver, comprising: a firstamplifier configured to produce a first stage signal by amplifying aradio frequency signal; a radio frequency filter; a second amplifier; asignal level detector configured to assert a bypass signal only when theradio frequency signal is sufficiently strong such that a threshold isreached; a switch configured to provide a switched signal, wherein whenthe bypass signal is asserted the switched signal is substantially thefirst stage signal without being filtered by the radio frequency filter,and when the bypass signal is not asserted the switched signal is thefirst stage signal filtered by the radio frequency filter and amplifiedby the second amplifier; and wherein the radio frequency signal is acode division multiple access (CDMA) signal and the bypass signal isasserted for a signal strength corresponding to a received signal ofminus 90 dBm.
 2. A radio frequency receiver, comprising: a firstamplifier configured to produce a first stage signal by amplifying aradio frequency signal; a radio frequency filter; a second amplifier; asignal level detector configured to assert a bypass signal only when theradio frequency signal exceeds a threshold; a switch configured toprovide a switched signal, wherein when the bypass signal is assertedthe switched signal is substantially the first stage signal withoutbeing filtered by the radio frequency filter, and when the bypass signalis not asserted the switched signal is the first stage signal filteredby the radio frequency filter and amplified by the second amplifier; aradio frequency to intermediate frequency converter configured toreceive the switched signal and to convert it to a first intermediatefrequency signal; and an intermediate frequency filter configured tofilter the first intermediate frequency signal to produce a secondintermediate frequency signal; wherein the signal level detector assertsthe bypass signal based on a level of the second intermediate frequencysignal.
 3. A radio frequency receiver, comprising: a first amplifiermeans for producing a first stage signal by amplifying a radio frequencysignal; a radio frequency filter means; a second amplifier means; asignal level detector means for asserting a bypass signal only when theradio frequency signal reaches a threshold; a switch means for providinga switched signal, wherein when the bypass signal is asserted theswitched signal is substantially the first stage signal without beingfiltered by the radio frequency filter means, and when the bypass signalis not asserted the switched signal is the first stage signal filteredby the radio frequency filter means and amplified by the secondamplifier means; and wherein the radio frequency signal is a codedivision multiple access (CDMA) signal and the bypass signal is assertedfor a signal strength corresponding to a received signal of minus 90dBm.
 4. A method of receiving a radio frequency signal, comprising:amplifying the radio frequency signal without filtering to produce afirst signal; filtering and amplifying the first signal to produce asecond signal; detecting a signal level corresponding to the radiofrequency signal; asserting a bypass signal only when the signal levelis sufficiently strong such that a threshold is exceeded; switchingbetween the first signal when the bypass signal is asserted, and thesecond signal when the bypass signal is not asserted; and wherein theradio frequency signal is a code division multiple access (CDMA) signaland the bypass signal is asserted for a signal strength corresponding toa received signal of minus 90 dBm.
 5. A radio frequency receiver,comprising: a first radio frequency amplifier, having a first biaslevel, configured to produce a first stage signal by amplifying an inputsignal; a radio frequency filter; a second radio frequency amplifier,having a second bias level; a signal level detector configured toproduce a bypass signal only when a first signal strength of thereceiver is sufficiently strong such that a threshold is reached, and toproduce a bias control signal according to a second signal strength ofthe receiver; and a switch configured to provide a switched signal,wherein when the bypass signal is asserted, the switched signal issubstantially the first stage signal without being filtered by the radiofrequency filter, and when the bypass signal is not asserted, theswitched signal is the first stage signal filtered by the radiofrequency filter and amplified by the second amplifier; a first biasgenerator configured to generate the first bias level according to thebias control signal; and a second bias generator configured to generatethe second bias level according to the bias control signal.
 6. Thereceiver of claim 5, wherein the radio frequency filter is atransmission rejection filter and the receiver is used in a transceiver.7. The receiver of claim 5, wherein the radio frequency signal is a codedivision multiple access (CDMA) signal.
 8. The receiver of claim 5,wherein the radio frequency signal is a code division multiple access(CDMA) signal and the bypass signal is asserted for a signal strengthcorresponding to a received signal of minus 90 dBm.
 9. The receiver ofclaim 5, wherein the first signal strength and the second signalstrength are the same.
 10. The receiver of claim 5, wherein the firstsignal strength is based on a signal from one stage of the receiver andthe second signal strength is based on a signal from another stage ofthe receiver.
 11. The receiver of claim 5, wherein the signal leveldetector is further configured to produce the bias control signal basedon the first signal strength and based on the bypass signal.
 12. Thereceiver of claim 5, wherein: the first signal strength is based on asignal from a first stage of the receiver; the second signal strength isbased on a signal from a second stage of the receiver, the second stagebeing subsequent to the first stage; and the signal level detector isfurther configured to produce the bias control signal based on the firstsignal strength and based on the bypass signal.
 13. The receiver ofclaim 5, wherein at least one of the bias generator circuits comprise avariable resistance circuit.
 14. The receiver of claim 5, wherein atleast one of the bias generator circuits is configured to shut down inresponse to a shutdown control signal.
 15. The receiver of claim 5,further comprising: a bias adjustment circuit configured to receive thebias control signal from the detector and to adjust the bias controlsignal prior to use by the bias generators.
 16. The receiver of claim15, wherein the bias adjustment circuit comprises a circuit selectedfrom an operational amplifier circuit and a sample and hold circuit. 17.The receiver of claim 15, wherein the configuration of the biasadjustment circuit is selected from a configuration that conditions thebias control signal, a configuration that scales the bias controlsignal, a configuration that responds to the bias level as regulatingfeedback, a configuration that holds the bias level at a particularlevel when the receiver is operating under an idle condition, and aconfiguration that holds the bias level at a particular level when thereceiver is operating under an idle condition and that generallyincreases the bias level as the signal strength increases.
 18. A radiofrequency receiver, comprising: a first radio frequency amplifier means,having a first bias level, for producing a first stage signal byamplifying an input signal; a radio frequency filter means; a secondradio frequency amplifier means, having a second bias level; a signallevel detector means for producing a bypass signal only when a firstsignal strength of the receiver exceeds a threshold, and for producing abias control signal according to a second signal strength of thereceiver; and a switch means for providing a switched signal, whereinwhen the bypass signal is asserted, the switched signal is substantiallythe first stage signal without being filtered by the radio frequencyfilter means, and when the bypass signal is not asserted, the switchedsignal is the first stage signal filtered by the radio frequency filtermeans and amplified by the second amplifier means; a first bias meansfor generating the first bias level according to the bias controlsignal; and a second bias means for generating the second bias levelaccording to the bias control signal.
 19. The receiver of claim 18,wherein the radio frequency filter means is a transmission rejectionfilter and the receiver is used in a transceiver.
 20. The receiver ofclaim 18, wherein the radio frequency signal is a code division multipleaccess (CDMA) signal.
 21. The receiver of claim 18, wherein the radiofrequency signal is a code division multiple access (CDMA) signal andthe bypass signal is asserted for a signal strength corresponding to areceived signal of minus 90 dBm.
 22. The receiver of claim 18, whereinat least one of the bias generator circuits is configured to shut downin response to a shutdown control signal.
 23. The receiver of claim 18,wherein: the first signal strength is based on a signal from a firststage of the receiver; the second signal strength is based on a signalfrom a second stage of the receiver, the second stage being subsequentto the first stage; and the signal level detector is further configuredto produce the bias control signal based on the first signal strengthand based on the bypass signal.
 24. The receiver of claim 18, furthercomprising: a bias adjustment means for adjusting the bias controlsignal from the detector means prior to use by at least one of the biasgenerator means.
 25. The receiver of claim 24, wherein the biasadjustment means comprises a circuit selected from an operationalamplifier circuit and a sample and hold circuit.
 26. The receiver ofclaim 24, wherein the bias adjustment means is selected from a means forconditioning the bias control signal, a means for scaling the biascontrol signal, a means for responding to the bias level as regulatingfeedback, a means for holding at least one of the bias levels at aparticular level when the receiver is operating under an idle condition,and a means for holding at least one of the bias levels at a particularlevel when the receiver is operating under an idle condition and thatgenerally increases the bias level as the signal strength increases.